What's the real unit of the particle system's start size

Hi,
I am using unity3d-4.3.4f1, and the Shuriken Particle System.

When I set the Max Particle Size in the Renderer submodule to 1, and set the start size to 1 too, the result is:

When I set the start size to 100, the result is :

The result is confusing me, Why the result is like this? The tool tip for Max Particle Size is said that the valid value is 0 to 1, and relative to the viewport, but you can see the result is not like as it said.

Am I in the wrong way?

Would you tell me the reason?
Thank you for your time!

this seems to be 2D and the second image looks closer this only is a result of the size of 100 units by 100 units in the first image it is only 1 unit by 1 unit therefore it is 1 square meter where as the other is 10 000 meters square